This invention relates to an acoustooptic device for use in controlling a laser beam to deflect or modulate the same in the device.
As will later be described with reference to a few figures of the accompanying drawing, a conventional acoustooptic device of the type described comprises an acoustooptic medium of, for example, a fused quartz and a transducer of, for example, a single crystal of lithium niobate attached to the acoustooptic medium. A combination of the acoustooptic medium and the transducer will be called an acoustooptic element hereinafter. With this structure, the transducer is supplied with an electrical signal or electric power to transform the electric signal into an ultrasonic wave which is propagated into the acoustooptic medium. Under the circumstances, an incident laser beam is incident onto the acoustooptic medium through an incident surface and is controlled by the ultrasonic wave to be emitted from the acoustooptic medium in the form of a diffracted beam or beams. For brevity of description, consideration will be made only about a first-order diffracted beam which is most important for such an acoustooptic device, although specific explanation will not be described.
In general, an acoustooptic device is evaluated by a diffraction efficiency which is given by the ratio of intensity between the incident and the diffracted laser beams. The diffraction efficiency is increased with an increase of the electric power supplied to the transducer.
Herein, it is to be noted that the electric power is finally converted in the acoustooptic medium into heat due to absorption of the ultrasonic wave of the acoustooptic medium and due to free vibration of the transducer. Consequently, the acoustooptic medium is heated to a temperature such that the acoustooptic medium is broken or destroyed.
In order to protect the acoustooptic medium from such destruction or breakage, a heat sink is usually attached to the acoustooptic element. More particularly, the heat sink has a cooling path formed therein and is brought into contact with the acoustooptic medium. A coolant, such as water, flows through the cooling path to cool the acoustooptic medium. In this situation, the acoustooptic medium is not kept in direct contact with the coolant and is, therefore, indirectly cooled by the coolant through the heat sink. Consequently, the cooling or cold efficiency is not particularly good and the acoustooptic medium therefore can not be kept at a low temperature. As a result, restriction is imposed on the electric power supplied to the acoustooptic medium which makes it difficult to obtain a high diffraction efficiency.